Size-dependent nanoconfinement effects in magnesium hydride

Nanoconfinement effect is crucial to improve the dehydrogenation kinetics of MgH2. However, the underlying micro-mechanism for nanoconfinement effect of carbon-based carrier on MgH2 nanoparticles is still ambiguous, hindering the design of carbon-based nanoconfined MgH2 nanoparticles. To address this dilemma, we applied density functional theory (DFT) calculations to investigate the interaction between carbon-based carrier and MgH2 nanoparticles. To analyze this issue, we designed various systems of carbon nanotubes nanoconfined MgH2 nanoparticles, with the range of particle size/pore size ratio from 0.3 to 0.8. The interaction strength between carbon-based carrier and MgH2 nanoparticles gradually increases with the increase of particle size/pore size ratio, and the dehydrogenation temperature decreases with the increase of particle size/pore size ratio. The electron of carbon-based carrier will transfer to MgH2 nanoparticles, leading to the weakening of Mg-H bonds. The weakened Mg-H bonds corresponding to lower dehydrogenation barrier, which is consistent with the phenomenon that the dehydrogenation temperature is inversely proportional to particle size/pore size ratio in calculations and experiments. This work not only elucidates the size-dependent nanoconfinement effects on MgH2 from a microscopic perspective, but also provides the theoretical basis for the design and development of carbon-based nanoconfined MgH2 nanoparticles.